Print hammer having braking means



Nov. 7, 1967 A. BELSON 3,351,006

PRINT HAMMER HAVING BRAKING MEANS Filed June 11, 1964 5| P4 FIG. 18

IN VENTOR ROSSABELSON ATTORNEY United States Patent o 3 351 006 PRINT HAMMER HAVIlVG zBRAKlNG MEANS Ross A. Belson, Framingham, Mass., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed June 11, 1964, Ser. No. 374,339 19 Claims. 01. 101-93) print hammers are very severe. Precise control of the time of arrival of the print hammer at the moving type carrier is necessary to avoid positional variations. The

exercise of such control on a repetitive basis requires the application of the same forcefrom the same reference position each time the print hammer is actuated.

In one embodiment'of a high-speed printer, the print hammer is spring-biased to the rest position into contact with an actuator arm that abuts a back stop. By energizing the actuator arm, the print hammer is propelled forward against the moving type carrier, from which it rebounds to return to its rest position, in part under the influence of the biasing springs. The hammer return normally occurs at a high velocity so as to cause further rebounding when the rear impact surface of the print hammer meets the actuator arm. The second rebound isin a forward direction and, if sufliciently large, may cause shadow printing or ghosting on the paper. If the print hammer is again propelled forward by the actuator arm while it is still rebounding, to before it has settled in its rest position, neither the amount of force imparted to the print hammer, nor its total travel will be the same as during the previous hammer actuation. Accordingly, the flight time of the print hammer, and hence its arrival at the type carrier, will be different and will result in a positional variation of the printed character from the norm. If the type carrier is a rotating type roll whose raised characters move columnarly past each print hammer at the print station, any variation of the flight time of the latter will result in the printing of the character above or below the print line. If the type carrier is in the form of a chain or belt which moves parallel to the aligned row of print hammers at the print station, variations in the flight time of a print hammer will result in a variable positioning of the printed character along the print line.

In a 1000-line-per-minute printer which uses a type roll as described above, actual printing for each line may occur during a period of the order of milliseconds, succeeded by a period for paper feeding of the order of 15 milliseconds. It is during the latter period that the print hammers must settle in their rest positions in time to meet the worst-case condition, when the last print hammer to be actuated during the previous print. cycle is actuated first in the next print cycle. Clearly, if higher printing speeds are to be achieved by shortening the print and paperfeed cycles, the hammer rebounding interval following hammer actuation must not be the limiting condition.

Various damping techniques have been proposed to quench print hammer rebound oscillations more quickly but none, to date, have provided completely satisfactory performance. In one such hammer damping arrangement, an elastic material is positioned between each actuator arm back stop and a fixed support, to absorb the shock of the returning hammer transmitted through the back stop. Past experience has shown that, during high-speed operation of such an arrangement, hammer oscillations may still be present under worst-case conditions to vary the an-ival time of the hammers at the print roll during the subsequent print cycle. Apart from the fact that such arrangement is expensive to implement since each back stop must be individually provided, the rest position of the hammer has a tendency to shift with repeateduse due to the compaction of the elastic material. 'Such a change increases the distance each hammer has to travel and, since it may vary from hammer to hammer dependent on the amount of use, it contributes to variations of the respective hammer flight times.

A further disadvantage derives from the fact that no control over the damping characteristics can be exer cisedonce the elastic material is installed. For example, if it is necessary to exchange the hammers there may be sufficient difference in their characteristics to require a changein the amount of damping required. Where an elastic damping material is used behind each, back stop,

such a change cannot be readily carriedout.

Accordingly, it is the primary object ofthe present invention to provide a print hammer damping arrangement which overcomes the foregoing disadvantages.

It is another object of the present invention to provide a print hammer damping mechanism in a high-speed printer for rapid-1y settling the oscillations of the returning print hammers.

It is a further object of the present invention to provide a print hammer damping arrangement for a highspeed printer which is simple in construction and economical to implement.

, It is an additional object of the present invention to provide a damping arrangement for rapidly settling the rebound oscillations of a moving member whose damping characteristics are adjustabl The foregoing objects of the present invention, together with the features and advantages thereof, will become apparent from the following detailed specification with reference to the accompanyingdrawings in which:

FIGURES 1A and 1B illustrate a preferred embodiment of the present invention; and FIGURES 2A and 2B illustrate another embodiment of the invention.

The print hammer 10 is seen to have a forward section 16 and a. rear section 18 connected by a central shank 20. All portions of the print hammer are of uniform thickness. The forward print hammer section terminates in a concave striking surface 22 which faces the type characters 14 as they rotate past the print station. The rear hammer section 18 terminates in a convex impact surface 24 which, when the hammer 10 is in the rest position shown in FIGURE 1A, abuts an actuator arm 26. The latter in turn rests against a fixed back stop 28. The hammer 10 is supported on a pair of leaf springs 30 which are aflixed to the hammer front and rear sections respectively, as well as to a fixed hammer support 32. The actuator arm 26 is rotatably disposed about a pivot 34, the lower arm portion facing a solenoid 36. A signal S may be selectively applied to the terminals of a solenoid winding 38.

The front and rear hammer sections 16 and 18 respectively, further include a pair of planar raised surfaces 49 and 42 respectively, which project above the corresponding surf-ace 21 of the shank 20. A horse shoe electromagnet 44 is positioned to one side of the print hammer 20 and has a pair of pole faces 46 and 48. The configuration of the pole face 46 is such that, in the rest position of the print hammer, it is positioned opposite the front sect-ion surface 40 to define a gap 47 therebetween of substantially uniform width. The pole face 48 is positioned opposite the rear hammer surface 42 to define a uniform gap 49 of substantially the same width as the gap 47. A signal source 51 is connected across the terminals of a winding 53 of the magnet 44 and is selectively adapted to provide an under-damped current waveform 55, as shown in FIGURE 1A. The applied signal may be varied as to amplitude and duration to obtain the desired damping characteristics.

The arrangement illustrated in FIGURE 1A is substantially repeated 132 times in the preferred embodiment of the invention, with respective print hammers aligned in a row side by side. Each print hammer is supported on a pair of leaf springs and sufficient clearance exists between them to permit hammer movement. A single magnet 44 is preferably employed, which runs the length of the entire row of print hammers, so that successive print hammers are positioned opposite different portions of the same pair of pole faces 46 and 4-8. Each support 32 may either carry a single print hammer, or a modular arrangement may be used wherein more than one print hammer is carried by a single support. The actuator arms 26 of successively positioned print hammers may alternately extend from above and below in FIGURE 1A, so as to obtain the requisite spacing to accommodate each solenoid 36.

In the hammer rest position which is illustrated in FIGURE 1A, the convex impact surface 24 is in contact with the actuator arm 26, which in turn rests against the fixed back stop 28. The leaf springs 30 are either perpendicular to the support 32 in the rest position, or they are tilted slightly in a forward direction, i.e. toward the type roll 12, in order to apply the requisite bias to the print hammer 10 to urge it to the rest position. The spacing of the concave hammer striking surface 22 from the raised characters 14 in the hammer rest position, is determined by the number of copies to be printed simultaneously which, together with interleaved sheets of carbon paper and an inked ribbon, must be accommodated therebetween.

When a signal S is applied to the winding 38 of any solenoid 36 during the print cycle, the corresponding actuator arm 26 is attracted and pivots forward about its pivot pin 34. The forward movement of the actuator arm 25, which is in contact with the convex impact surface 24 in the rest position of the hammer 10, causes the latter to be propelled forward as illustrated in FIGURE 1B. In a preferred embodiment of the invention, the movement of the actuator arm 26 is limited so that the print hammer 10 travels forward toward the type roll 12 under its own momentum and at high velocity to drive the intermediately positioned paper and ribbon against the latter. Upon rebounding off the type roll, the hammer returns toward its rest position, to which it is urged by the leaf springs 30. In its rearward travel, the hammer 10 also returns the actuator 26 into contact with the back stop 28.

The return movement of the hammer to its rest position occurs at approximately one-half the incident velocity. Hammer rebounding off the actuator 26 and subsequent hammer oscillations must be suppressed as quickly as possible during the paper feed cycle in order to ready the hammer for printing during the next print cycle. To this end, a damping signal, having an underdamped waveform 55, is applied to the magnet winding 53- at the termination of each print cycle. This damping signal sets up a flux path which includes the magnet 44, the hammer 10 and the two flux gaps 47 and 49. The gapbridging flux lines, which are indicated by dotted lines, in the drawings, have their minimum length in the hammer rest position shown in FIGURE 1A, so that the overall flux path similarly is at a minimum then.

While the length of the flux path in the gap 49 remains the same in the forward hammer position illustrated in FIGURE 1B, the width of the gap 47 is non-uniformly increased and the flux path in the gap 47 is materially greater than that prevailing in the hammer rest position. The length of the over-all flux path is therefore increased and a force is set up to return the hammer to its rest position. This behavior is due to the minimum reluctance principle whereby the flux has a tendency to seek the shortest path. Since the flux path in the gap 47 has its minimum length when the hammer is in its rest position, the effect of the flux will be to oppose a further rebound of the returning hammer off the hammer actuator 26.

It will be noted that the damping action is controllable in degree and in time by controlling the damping signal which is applied to the winding 53. The maximum amplitude of the applied signal, which may be of the order of 3 to 4 amperes, will depend on the desired damping characteristic of the overall arrangement. The damping signal is applied only during the paper feed cycle. Thus, there is no interference with the forward hammer movement during the print cycle. It will be understood that the damping signal being applied immediately following the termination of the preceding print cycle, acts to settle only the hammers which are still oscillating at such time. Those hammers which are actuated early in the print cycle will normally have settled to their rest position at end of the print cycle.

The actuator arm 26 is seen to be positioned in close proximity to the aforesaid flux path, but is preferably excluded therefrom for efiicient operation. Accordingly, the arm 26 may consist of stainless steel whose permeability is low compared to the permeability of the hammer 10 which may consist of hardened steel. The end of the actuator arm 26, which is in contact with the hammer impact surface 24, may be treated to lower its permeability still further.

FIGURES 2A and 2B illustrate a further embodiment of the present invention, applicable reference numerals having been retained. A toro'id-like magnet 58 is employed whose pole faces 54 and 56 are positioned at right angles to each other. As in the embodiment of FIGURES 1A and 1B, the pole faces 54 and 56 run the entire length of the aligned row of print hammers 10. In this embodiment, each print hammer carries a flag 52 consisting of a highpermeability material, which is positioned between the pole faces 54 and 56 in the hammer rest position shown in FIGURE 2A. A pair of uniform gaps 60 and 62 is defined between a pair of mutually perpendicular flag surfaces 57, 59 and the pole faces 54 and 56 respectively.

FIGURE 2B illustrates the forward hammer position. The pole face 54 now faces only a portion of the flag surface 57. Accordingly, some of the flux flowing through the pole face 54 now links the surface 59 and another portion of the flux directly links the pole face 56. The width of the pulse gap 60 is therefore non-uniformly increased. Similarly, the width of the flux gap 62 is greater when the hammer 10 is in its forward position than in the rest position.

An important advantage of the arrangement illustrated in FIGURE 2 resides in the fact that the print hammer and the actuator arm may be effectively excluded from the magnetic flux path, which now includes only the magnet 58, the gaps 6t and 62 and the flag 52. Since the latter is not subject to the requirements which are applicable to the hammers, it may consist of a high-permeability material so that greater sensitivity is obtained and the damping action is more readily effected.

It will be readily realized that the present invention is V i susceptible of operating in different environments and may itself be modified, dependingon the particular operating conditions under which it is to be employed. For

example, the damping arrangement herein disclosed may find application in chain printers where rapid settling of the hammer oscillations is similarly required. The physical configuration of the hammers may vary, provided only that a projection is provided which is flux-link'ed to a magnetic pole through a variable gap. The hammer itself need not be supported on leaf springs, as shown,

but may travel in a set of guides, urged to a rest position by resilient means. Similarly, the actuation of the ham-.

milliseconds, as compared to intervals of milliseconds and more required in prior art devices. Under these conditions print hammer rebounding is no longer a limitation on the increase in printing speed, as is the case in prior art damping arrangements. In' additionto its simplicity, the present invention provides controllable damping to suit the requirements of different operating conditions."

Moreover, the use; of one magnet which spans the entire row of print hammers permits the implementation of the invention at relatively low cost.

From the foregoing disclosure of the invention it will be apparentthat numerous modifications and departures may now occur to those skilled in the art, all of which fall within the spirit and scope contemplated by the invention.

What is claimed is:

1. A damping mechanism comprising a component movable between two extreme positions, means for resiliently urging said component to one extreme position, means for selectively driving said component to said other extreme position, and means for damping out the oscillations of said component upon its return to said one extreme position, said damping means comprising a magnetically passive projection of relatively high permeability on said component, and magnet means external to said component adapted to provide a mag netic field, said magnet means having at least one magnetic pole positioned opposite said projection and spaced therefrom in said one extreme position to'provide a variable reluctance flux path, including said projection, which has its minimum reluctance in said one extreme position.

2. The apparatus of claim 1 wherein said magnet means external to said component comprises a magnetic core and an associated winding, and a variable signal source adapted to energize said winding.

3. In an on-the-fiy printer, a print station, a type roll rotatably adapted to present diiferent characters to said print station for printing on an intermediately positioned paper web, said print station including a plurality of aligned hammers of relatively high permeability each comprising an elongated structure of uniform width having front and rear sections connected by a central shank, said front section having a concave forward surface facing said type roll and spaced therefrom, said rear section having a convex rear surface, said front and rear sections each having parallel upper and lower surfaces lying in a pair of common planes disposed above and below respectively, corresponding surfaces of said central shank, a support parallel to said planes,'a pair of parallel leaf springs transverse to said planes and coupling said bottom surfaces to said support to permit movement of said hammer in a direction substantially parallel to said planes, a magnet including first and second pole faces positioned opposite respective ones of said pair of co-planar upper surfaces in the rest position of said-hammer to define first and second gaps respectively of uniform width therebetween, and an actuator arm selectively adapted to strike said convex rear surface to drive said hammer forward against said type roll, the forward movement of said hammer causing the upper surface of said central member to move at least partly opposite said first pole surface to:

increase the effective length of the flux path in said first gap.

4. The apparatus of claim 3 wherein said magnet includes a winding, and a variable signal source adapted to energize said winding.

5. The apparatus ofclaim 3 wherein said magnet includes a Winding, and a current source selectivelyadapted V to energize-said winding.

6. The apparatus of claim 3 wherein said hammer con. sists of a material whose permeability is large relative to that of said actuator arm.

7. In an on-the-fly printer, a print station, a type carrier movably adapted to present different type characters to said print station for printing on an intermediately positioned paper web, said print station comprising a plurality of aligned, elongated print hammers of relatively high permeability each having a striking surface facing said type characters and a rear impact surface, a pair of raised surfaces on one side of each hammer lying in a common plane spaced from the central hammer structure th'erebetween, a pair of spaced leaf springs anchored in the other side of each hammer transverse thereto, said leaf springs being further anchored in a fixed support and permitting substantially linear hammer movement toward said type roll from a resiliently maintained rest position, a magnet disposed on said one side of each hammer and including a pair of pole faces uniformly spaced from and opposite to said raised surfaces when said hammer is in its rest position, and an actuator selectively adapted to strike said rear impact surface to drive saidhammer forward against said type characters, thereby moving said central hammer structure at least partly opposite one of said polefac es.

I 8. A high-speed printer comprising a platen, a print station including a print hammer resiliently urged to a rest position, means for selectively driving said hammer out of said rest position against said platen to print on an intermediately positioned paper web, means for damping out hammer oscillations upon the return of said hammer to said rest position, said damping means comprising at least one magnetically passive projection of relatively high permeability on said hammer, and magnet means external to said hammer adapted to provide a magnetic field, said magnet means including a magnetic pole positioned opposite said hammer projection and spaced therefrom in the hammer rest position to provide a variable reluctance flux path, including said projection, which has its minimum reluctance in said rest position.

9. In an on-the-fly printer, a print station, a type carrier movably adapted to present different characters to said print station for printing on an intermediately. positioned paper web, said print station comprising a plurality of elongated, aligned hammers each having a striking surface facing said characters, each of said hammers being supported on a pair of transverse leaf springs resiliently urging it to a rearward hammer rest position but permit ting forward hammer movement, means for selectively driving said hammers out or said rest position against said characters, and means for damping out hammer oscillations upon the return of each hammer to its rest position, said damping means comprising at least one magadapted to propel said hammer forward, a back stop, said hammer urging said actuator arm against said back stop in said rest position.

11. The apparatus of claim wherein each of said actuator arms consists of a material whose permeability is low compared to that of said hammers.

12. The apparatus of claim 9 wherein said magnet means external to said hammers comprises a magnetic core and an associated winding, and a variable Signal source adapted to energize said winding.

13. The apparatus of claim 9 wherein each of said hammers includes a pair of projections terminating in a pair of co-planar surfaces spaced from a parallel surface of an intermediately positioned central hammer portion, said magnet means external to said hammers including a pair of magnetic poles terminating in a pair of pole faces positioned opposite respective ones of said pair of coaplanar surfaces to define a pair of gaps of uniform width in said hammer rest position, said forward hammer movement causing the effective width of at least one of said gaps to be non-uniformly increased by bringing said central hammer portion surface at least partly opposite one of said pole faces.

14. The apparatus of claim 13 wherein said hammers are aligned in a row, said pole faces extending the length of said hammer row.

15. In an on-the-fly printer, a print station, a type carrier movably adapted to present different characters to said print station for printing on an intermediately positioned paper web, said print station comprising a plurality of elongated, aligned hammers each having a striking surface facing said characters, each of said hammers being supported on a pair of transverse leaf springs resiliently urging it to a rearward hammer rest position but permitting forward hammer movement, means for selectively driving said hammers out of said rest position against said characters, means for damping out hammer oscillations upon the return of each hammer to its rest position, said damping means comprising a substantially toroidal, magnetic core terminating in a pair of mutually perpendicular pole faces, and at least one projecting flag on each hammer including a pair of surfaces substantially parallel to respective ones of said pole faces and uniformly spaced therefrom in said hammer rest position, each of said flags providing a flux path with said core which has its minimum length in said hammer rest position.

16. The apparatus of claim 15 wherein said hammers are aligned in a row, said pole faces extending the length of said hammer row.

17. The apparatus of claim 15 wherein said core and said flag consist of a magnetic material having a permeability which is substantially greater than that of said hammer.

18. In an on-the-fiy printer, a print station, a type roll rotatably adapted to present different rows of identical characters to said print station for printing on an intermediately positioned paper web, said print station comprising a plurality of elongated print hammers of uniform thickness aligned in a row parallel to the axis of said type roll, each of said hammers including front and rear hammer sections connected by a central shank, said front hammer section having a concave striking surface facing said type roll and upper and lower surfaces spaced respectively above and below corresponding surfaces of said shank, said rear hammer section terminating in a convex impact surface and including upper and lower surfaces coplanar with the corresponding surfaces of said front section, a fixed support spaced from said lower surfaces and parallel thereto, a pair of leaf springs corresponding to each hammer and having their ends anchored in said lowor surfaces and in said support respectively, each pair of leaf springs resiliently urging its hammer to a rest position but permitting forward hammer movement toward said type roll, an actuator corresponding to each hammer including a pivoted arm consisting of a material whose permeability is high relative to that of said hammer, a back stop, said hammer impact surface bearing against said actuator arm in said rest position to urge the latter against said back stop, solenoid means for selectively r0 tating said actuator arm about its pivot to drive said hammer against said type roll, and means for damping out hammer oscillations upon the return of each hammer to said rest position, said damping means including a horse shoe magnet having first and second pole faces extending the length of said hammer row, each of said pole faces being positioned directly opposite one of each pair of said upper hammer surfaces in the rest position of the corresponding hammer and being uniformly spaced therefrom to provide a pair of flux paths through said upper hammer surfaces, at least one of which has its minimum length in said hammer rest position, said one flux path at least partly including the upper surface of said central shank during said forward hammer movement.

19. The apparatus of claim 18 wherein said magnet includes a winding and a variable current source selectively adapted to energize said winding.

References Cited UNITED STATES PATENTS 2,708,737 5/1955 Skidmore 310-93 X 2,787,210 4/1957 Shepard 101-93 2,788,457 4/1957 Griest 317-123 X 2,951,955 9/1960 Crowder 310-93 3,072,045 1/1963 Goin 101-93 3,144,821 8/1964 Drejza 101-93 3,172,352 3/1965 Helms 101-93 3,172,353 3/1965 Helms 101-93 3,199,650 8/1965 Brown et al. 101-93 X EUGENE R. CAPOZIO, Primary Examiner.

ROBERT E. PULFREY, Examiner.

P. R. WOODS, E. S. BURR, Assistant Examiners. 

1. A DAMPING MECHANISM COMPRISING A COMPONENT MOVABLE BETWEEN TWO EXTREME POSITIONS, MEANS FOR RESILIENTLY URGING SAID COMPONENT TO ONE EXTREME POSITION, MEANS FOR SELECTIVELY DRIVING SAID COMPONENT TO SAID OTHER EXTREME POSITION, AND MEANS FOR DAMPING OUT THE OSCILLATIONS OF SAID COMPONENT UPON ITS RETURN TO SAID ONE EXTREME POSITION, SAID DAMPING MEANS COMPRISING A MAGNETICALLY PASSIVE PROJECTION OF RELATIVELY HIGH PERMEABILITY ON SAID COMPONENT, AND MAGNET MEANS EXTERNAL TO SAID COMPONENT ADAPTED TO PROVIDE A MAGNETIC FIELD, SAID MAGNET MEANS HAVING AT LEAST ONE MAGNETIC POLE POSITIONED OPPOSITE SAID PROJECTION AND SPACED THEREFROM IN SAID ONE EXTREME POSITION TO PROVIDE A VARIABLE RELUCTANCE FLUX PATH, INCLUDING SAID PROJECTION, WHICH HAS ITS MINIMUM RELUCTANCE IN SAID ONE EXTREME POSITION. 